1. Field of the Invention
The present invention relates to a file security system in which it has been made possible that enciphered data are stored in a storage medium and said data are deciphered only by the deciphering means specifically kept secret.
2. Prior Art
Heretofore, in order to prevent information from being disguised or disclosed, the technique of keeping enciphered information in custody has been widely put to practical use not only for military but also for civilian purposes, and as an algorithm for the enciphering, for instance, Data Encryption Standard (DES) was published in the United State of America in 1977.
Accordingly, in the case where a writing (plaintext) which one can read and understand is to be enciphered as occasion demands, it has been devised in such a way that the plaintext is enciphered and written in an auxiliary storage means by driving the encryption unit through the user's application program by utilizing, for instance, the above-described Data Encryption Standard, and then the "key" composed of one kind of random number used in the above-described algorithm is utilized to achieve the deciphering. Thus, as the user, only the information whose enciphering desired could be enciphered and deciphered.
Further, as one of the commercialized techniques of information transfer according to such DES there is known, for instance, the Bank of Japan Finance Network System.
The characteristic points in the above-described system are found in that in the case of data transmission, in order to prevent the surreptitious reading, disguise, or unjust input of the information the system is designed to encipher the information according to the above-described DES, and also in the case of data output, it is designed to prevent disguise of the information by making full use of the Message Authentication Code (MAC) which is unique character produced by enciphering techniques, thus ensuring the safety of information transmission as well as the proof of transaction.
Further, in the Credit and Finance Information System it is contemplated that the privacy of the user's information is strictly kept in such a way that by utilizing the terminal equipment the user's account number of sales telegram is enciphered and this information is communicated from the bank to the center of the above-described Credit and Finance Information System.
In the above-described techniques of keeping information secret, there have still remained the following problems to be solved.
In the first place, since the algorithm of the above-described Data Encryption Standard has now been prevailingly known, the users are taking pains to keep the above-described particular "key" secret for the maintenance of the privacy of information.
In the next place, with regard to, for instance, "the account number" or "the information retrievable by name" in the banking business the portion corresponding to the retrieving key cannot be enciphered as a matter of course, so that it is not possible in actuality to contemplate the enciphering of the whole information, rendering it inevitable to use the application program by particular programming.
Furthermore, in the case where as the storage medium for the information storage and transmission, use is made of the magneto-optical disk MOD which may also be called a floppy disk of an especially large capacity, it is convenient in that transportation is easy on account of its compactness, whereas there remain possibilities such that it can be readily carried away, misdelivered, and so on, and therefore, in the security management of information an original idea or a new device is found to be indispensable.